Osteoporosis is the name of a disease process characterized by the progressive loss of bone mass and deterioration of the micro architecture of the skeleton leading to increased bone fragility and risk of fracture. It is a silent disease that has usually progressed significantly by the time it is diagnosed. During most of our lives, the normal remodeling of bone results in considerable bone turnover but no net change in mass. In osteoporosis, the equilibrium of this process is disturbed - bone mass diminishes because of excessive loss of bone or inadequate new bone production.
Osteoporosis is a major health threat for more than 28 million Americans, especially women, in whom it is four times more common than men. It is the major cause of bone fractures in older people, causing over 1.2 million fractures each year. The National Osteoporosis Foundation says that one in two women and one in eight men over the age of 50 will have an osteoporosis related fracture in their lifetime.
Osteoporosis is not an inevitability that occurs as we age. It is a preventable disease. The increased public awareness, especially among women, about the risks of osteoporosis has made them aware of the preventive measures that can protect them at critical points in life such as the adolescent growth spurt and menopause. The combination of proper nutrition and weight-bearing exercise can maximize peak bone mass and prevent fractures later in life. There is no better example of the health benefits of fitness and nutrition than the role they play in preventing osteoporosis.
Physical activity, through its load-bearing effect on the skeleton, is likely the single most important influence on bone density and architecture, according to the U.S. Surgeon General’s Report on Physical Activity and Health.
The importance of skeletal health begins in youth. Exercise causing the most impact on the skeleton produces the greatest bone benefit. There are two forms of exercise that produce the greatest forces on the skeleton. The first type of exercise is weight-bearing exercise. This is any activity you do on your feet, that works your bones and muscle against gravity. Walking, jogging, dancing, and impact aerobics are excellent examples. Swimming and cycling are not weight-bearing activity. They are great for your heart but not but not for your bones. The second type of exercise most beneficial to your bones is strength-training exercise. Working against resistance, such as exercising with free weights or strength-training machines, strengthens both muscles and bones.
Adolescence (between the ages nine and 14) provides an incredible opportunity to see the influence of exercise on bone mass. A Finnish Study of women tennis players compared the bone mass of each woman’s racket arm with her non-dominate arm. The study found that women who started playing tennis after puberty had dominant arms with about 11 percent more bone mass. Those women who started playing tennis before puberty had dominant arms about 23 percent greater in bone mass. This study and several others have identified the pubertal growth spurt as a key time for women to achieve maximum bone mass. The National Osteoporosis Foundation research has determined that by the age of 20 the average women has reached 98 percent of her skeletal bone mass. After age 20, the key to avoiding osteoporosis is keeping the bone mass you have.
Studies of patients confined to bed and of astronauts in space revealed that both inactivity and the loss of gravity’s effect can lead to dramatic loss of bone. These again proved the strong relationship between physical activity and healthy bones.
It is never to late to begin a fitness program to keep your bones strong. We know that the decline in estrogen at menopause is another vital period time for women. It is not unusual for many women to lose up to 20 percent of their bone mass in the five to eight years after monthly cycles stop. The average age of menopause in American women is 50 years. The period just before menopause is the time when women need to dedicate themselves to keeping their bones strong by increasing fitness activity.
A study by Tufts University physiologist Miriam Nelson, published in the Journal of the American Medical Association, showed that postmenopausal women who performed just two 40-minute strength training sessions a week for one year gained one percent in bone density, while women in the sedentary control group lost two percent.
It is sometimes forgotten that bone is more than just a collection of calcium crystals. Bone is active living tissue, continually remodeling itself through bone forming and bone re-absorbing activity. Bone cells are constantly participating in a wide range of biochemical reactions. Like any living tissue, bone has diverse nutritional needs.
The two most well known nutrients essential to preventing osteoporosis are calcium and vitamin D. The vast majority of the mineral content in bone comes from calcium. According to a 1994 National Institutes of Health consensus conference, optimal calcium intake is the amount a person needs to reach maximum peak bone mass, maintain adult bone mass and minimize bone loss later in life. Obviously this means requirements vary throughout a person’s lifetime. The term adequate intake (AI) is the new term for the amount of calcium recommended by age per day. The following is a table listing the AI:
- 0-6 months 210 mg
- 6mos-12 months 270 mg
- 1-3 years 500 mg
- 4-8 years 800 mg
- 9-18 years 1,300 mg
- 19-50 years 1,000 mg
- 51 and over 1,200 mg
Most people get about 250 mg from their general diet each day and 300 mg for each serving of diary products each day. A study from 1998 showed that only 19 percent of adolescents were aware of the need for a daily consumption of calcium, and that the average calcium intake was about 50 percent of the recommended requirement.
There is abundant research that vitamin D deficiency is a major contributing factor in osteoporosis. Vitamin D is also a key requirement for intestinal calcium absorption. It is also converted in the kidneys to the steroid hormone required not only for bone development and growth in children, but also for maintenance of bone in adults. We get vitamin D by going out in the sunlight and from food. Foods such as diary products, eggs and fish contain little vitamin D and much more is needed. Fortunately, milk, infant formula and cereals are fortified with vitamin D. Several studies have shown that exposure to the sun is adequate only in equatorial regions. The estimated daily vitamin D intake among average Americans is 240 IU per day. The adequate intake for vitamin D everyone over the age of six months is at least 400 IU per day. The elderly should try to get 600 IU per day. The safety margin with vitamin D is substantial, complications do not occur unless the daily dose exceeds 2400 IU.
There are several other vitamins and minerals necessary for optimal bone health. Proper nutrition is needed to provide the vitamin K, folic acid, and vitamin B6 healthy bones require. Diet must provide other essential minerals besides calcium. Strong bones depend on adequate supplies of magnesium, manganese, zinc, boron, strontium and silicon.
It is also important to know that diets that are too high in salt or protein (particularly animal protein) can weaken bones.
As you can see, preventing osteoporosis depends on both regular exercise and proper nutrition. There is no substitute for the weight-bearing exercise and the strength-training exercise bones require. In addition, there is no substitute for eating the five servings of fresh fruit and vegetables, along with the three servings of diary products each day that a nutritionist would recommend. However, the realities of life prevent even the well intentioned from achieving close to those minimums. Therefore, there are significant benefits by taking a multivitamin and a calcium supplement. A nutritional supplement, especially in postmenopausal women, is now a medical standard of care. A multivitamin plus calcium insures that you receive the other necessary nutrients the body needs to keep our bones strong.
- Riggs BL, Melton LJ III. The prevention and treatment of osteoporosis. N Engl J Med 1992;327:620-627.
- American College of Sports Medicine position stand: Osteoporosis and exercise. Med Sci Sports Exerc 1995;27(4);i-vii.
- Gaby AR, Wright, JV. Nutrients and Bone Health. Nutrition Inst. Journ 1998.
- Reid IR, Ames RW, Evans MC, et al. Effects of calcium supplementation on bone loss in postmenopausal women. N Engl J Med 1993;328:460-464.
- Nattiv, A, Osteoporosis: Its prevention, recognition, and management. 1998 Fam Prac Recert; vol20,no2;17-41.